Re: [PATCH bpf-next] libbpf: keep FD_CLOEXEC flag when dup()'ing FD

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, May 29, 2024 at 03:32:39PM -0700, Andrii Nakryiko wrote:
> Make sure to preserve and/or enforce FD_CLOEXEC flag on duped FDs.
> Use dup3() with O_CLOEXEC flag for that.
> 
> Without this fix libbpf effectively clears FD_CLOEXEC flag on each of BPF
> map/prog FD, which is definitely not the right or expected behavior.

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

> 
> Reported-by: Lennart Poettering <lennart@poettering.net>
> Fixes: bc308d011ab8 ("libbpf: call dup2() syscall directly")
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---
>  tools/lib/bpf/libbpf_internal.h | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
> index a0dcfb82e455..7e7e686008c6 100644
> --- a/tools/lib/bpf/libbpf_internal.h
> +++ b/tools/lib/bpf/libbpf_internal.h
> @@ -597,13 +597,9 @@ static inline int ensure_good_fd(int fd)
>  	return fd;
>  }
>  
> -static inline int sys_dup2(int oldfd, int newfd)
> +static inline int sys_dup3(int oldfd, int newfd, int flags)
>  {
> -#ifdef __NR_dup2
> -	return syscall(__NR_dup2, oldfd, newfd);
> -#else
> -	return syscall(__NR_dup3, oldfd, newfd, 0);
> -#endif
> +	return syscall(__NR_dup3, oldfd, newfd, flags);
>  }
>  
>  /* Point *fixed_fd* to the same file that *tmp_fd* points to.
> @@ -614,7 +610,7 @@ static inline int reuse_fd(int fixed_fd, int tmp_fd)
>  {
>  	int err;
>  
> -	err = sys_dup2(tmp_fd, fixed_fd);
> +	err = sys_dup3(tmp_fd, fixed_fd, O_CLOEXEC);
>  	err = err < 0 ? -errno : 0;
>  	close(tmp_fd); /* clean up temporary FD */
>  	return err;
> -- 
> 2.43.0
> 
>